West Nile virus (WNV) is a single stranded, positive-sense RNA virus belonging to the genus Flavivirus (family Flaviviridae). Historically, human infections with WNV, a member of the Japanese encephalitis serocomplex, usually were associated with a mild undifferentiated fever (Monath and Heinz, 1996). However, recent outbreaks in Europe, Israel, and North America involving humans, equines, and birds have been associated with significant rates of neurological disease (Lanciotti et al., 1999; Solomon and Vaughn, 2002). Until 1999, the geographical distribution of the virus was limited to Africa, the Middle East, India, and western and central Asia with occasional epizootics and epidemics in Europe (Murgue et al., 2002). But since the summer of 1999, the distribution of WNV has expanded to include 46 states of the continental U.S. and seven Canadian provinces, as well as Mexico and most likely a number of Caribbean Islands (Estrada-Franco et al., 2003; Komar et al., 2003; Blitvich et al., 2003; Dupuis et al., 2003; Quirin et al., 2004). As WNV has spread across North America, the number of human and veterinary cases and deaths has continued to rise, resulting in the largest recorded epidemic of arboviral encephalitis in the western hemisphere during 2002 (CDC, 2002). Because of its relatively recent introduction, studies concerning the evolution of WNV are important to understand the extent to which the virus has mutated as its temporal and geographic distributions have expanded. Nucleic acid sequencing studies of WNV isolates collected across the U.S. since 1999 have identified mutations to the genome when compared to the prototype New York strain, WN-NY99, which may also be referred to as 382-99 (GenBank Accession No. AF196835; SEQ ID NO:1), which reveal the presence of distinct genetic variants that group in a temporally- and geographically-dependent manner (Beasley et al., 2003; Davis et al., 2003).
Following the introduction of WNV into Texas during 2002, studies were initiated to determine if phenotypic changes also occurred among the genetic variants. Although genetically distinct on a microevolutionary scale, previous studies indicated that the phenotypic characteristics (i.e., plaque morphology, in vitro growth kinetics, neuroinvasiveness and neurovirulence in a mouse model) of WNV isolates collected in 2002 were not significantly different from isolates collected in 1999 (Beasley et al., 2003).
U.S. 2004/0052818 relates to attenuated live vaccines comprising flavivirus mutants, of which West Nile virus is a specific embodiment. In a further specific embodiment, the flavivirus mutant has a deletion in the capsid protein of at least more than 4 successive amino acids such that the carboxy-terminal hydrophobic region is not affected by the deletion.
U.S. 2004/0037848 describes an immunogenic or vaccine composition for induction of an immune response or protective immune response against WNV in an animal. The compositions comprise a vector containing a heterologous nucleic acid molecule that expresses in vivo a WNV antigen, immunogen, or epitope, such as WNV E; WNV prM and E; WNV M and E; WNV prM; WNV prM-E; WMV M-E; or WMV prM-M-E. In specific embodiments, the vector is a recombinant viral vector.
U.S. Pat. No. 6,576,757 is directed to nucleic acids encoding a recombinant multivalent antigenic polypeptide that comprises multiple non-contiguous subsequences of at least a first antigenic flavivirus polypeptide and multiple non-contiguous subsequences of at least a second antigenic flavivirus polyeptide, wherein the recombinant antigenic polypeptide induces a immune response greater than one induced by any one of the first or second polypeptides.
WO 03/061555 describes West Nile virus vaccines, particularly for horses, wherein the vaccine comprises an immunogenically active component such as a live attenuated, inactivated, or killed whole or subunit WN virus; an antigen derived therefrom; DNA derived therefrom, such as plasmid DNA; and a mixture thereof.
Thus, the present invention addresses a need in the art to identify Flavivirus variants comprising phenotypic changes that result in attenuation, and particularly for their use in immunogenic compositions for therapeutic purpose.